Multilayer capacitors are used extensively in electrical circuits. Such capacitors, which comprise a plurality of alternating dielectric layers and conductive layers, the latter serving as internal electrodes, may be formed as rugged monolithic units with a very high capacitance per unit volume. A common procedure for their production comprises the casting of thin sheets of the desired dielectric ceramic composition in finely divided form, using a resin as a temporary bond. Metal-containing electroding paste is then deposited, frequently by a silk screen procedure, in predetermined areas on a plurality of the sheets, a number of electrode areas being produced on each sheet. The thus-coated sheets, after proper orientation and stacking are consolidated by pressure. Individual units are obtained by suitably cutting the green ceramic block of consolidated sheets. These units are subjected to a heating and firing procedure to burn off the combustible binders in the sheets and the electroding layers and to sinter the ceramic material whereby to obtain integral, dense, ceramic-metal structures. When the sheets are properly printed, oriented, stacked, and cut, the several electrode layers in each unit are so arranged that each layer is exposed only at an edge face of the unit and immediately adjacent electrode layers are exposed at opposite edge faces of the unit thus forming two sets of unconnected internal electrodes. Termination electrodes are then applied to the edge faces at which the electrodes are exposed to tie-together alternate internal electrodes electrically.
Since in the above-described process the ceramic and the internal electrodes are co-fired, the metal of the internal electrodes and the ceramic must be compatible at high temperatures, e.g. 1100.degree. C to 1400.degree. C, and the metal must be resistant to oxidation at those temperatures since the best dielectric properties of the ceramic are obtained when the firing is carried out in an oxidizing atmosphere. Consequently, manufacturing costs of such multilayer capaciters are high because high-melting noble metals such as palladium, platinum, and alloys thereof with gold must be used for the internal electrodes.
In U.S. Pat. No. 2,919,483, issued Jan. 5, 1960 to C. K. Gravley, a method is disclosed for producing multilayer ceramic capacitors which does not require the presence of internal metal electrodes while the ceramic is fired to mature it. More recently a method for producing multilayer ceramic capacitors and multilayer ceramic circuit boards using relatively inexpensive metals for internal electrodes has been disclosed in U.S. Pat. No. 3,679,950, issued July 25, 1972 to Truman C. Rutt. The procedure disclosed therein involves forming sintered ceramic units or chips having porous internal strata or layers alternating with dielectric layers, the porous strata being the same size and shape as the conventional noble metal electrodes and being oriented the same, i.e. with immediately adjacent ones having open ends at opposite edge faces of the chips. Metal is then introduces into the porous ceramic strata and termination electrodes are applied, thus forming multilayer capacitors. This method permits the use of such metals as lead, tin, or silver for internal electrodes. A similar procedure is employed in producing multilayer ceramic circuit boards that have internal conductors.
It has been found that a particularly convenient way to introduce metal into the porous strata or layers of ceramic units prepared as described in U.S. Pat. No. 3,679,950 whereby to form internal electrodes therein is by introducing the metal under pressure. However, a problem arises at times because the cooled metal from the metal bath employed may bond together two or more units. It is, therefore, desirable to keep the units separated while metal is introduced, but heretofore no entirely satisfactory method of accomplishing this has been found.
In the production of multilayer ceramic capacitors by prior known methods the provision of end termination has been a problem since an additional firing step is required and the electroding compositions used are expensive.